Positive electrode active material and preparation method therefor, positive electrode plate, battery cell, battery, and electrical apparatus

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode plate, a battery cell, a battery, and an electrical apparatus, and belongs to the technical field of batteries. The positive electrode active material comprises: a positive electrode matrix material, and a first coating layer and a second coating layer, sequentially coated on a primary particle surface of the positive electrode matrix material, the concentration of elemental lithium in the first coating layer being less than the concentration of elemental lithium in the positive electrode matrix material, and the second coating layer comprising an ion conductor material. The described technical solution can improve battery cell cycle performance.

Description

Positive electrode active material and preparation method thereof, positive electrode sheet, battery cell, battery, and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent document claims priority to and the benefit of Chinese patent application No. 202311571714.3, filed on November 22, 2023, entitled "Positive Electrode Active Material and Preparation Method Thereof, Positive Electrode Sheet, Battery Cell, Battery, and Electric Device." The entire contents of the aforementioned patent application are incorporated by reference into this patent document. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to a positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery cell, a battery, and an electrical device. Background Art

[0004] With the increasing severity of environmental pollution, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor in its development.

[0005] The development of battery technology requires consideration of multiple design factors, such as energy density, cycle life, and reliability. The design of the positive electrode active material in a battery cell is crucial to its performance. Therefore, how to provide a positive electrode active material that improves the cycle performance of the battery cell is a pressing technical issue.

[0006] Summary of the Invention

[0007] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode active material to improve the cycle performance of a battery cell.

[0008] In order to achieve the above-mentioned objectives, the present application provides a positive electrode active material and a preparation method thereof, a positive electrode plate, a battery cell, a battery, and an electrical device.

[0009] In a first aspect, a positive electrode active material is provided, comprising: a positive electrode base material, a first coating layer and a second coating layer sequentially coated on the surface of primary particles of the positive electrode base material; wherein the concentration of lithium element in the first coating layer is less than the concentration of lithium element in the positive electrode base material, and the second coating layer comprises an ion conductor material.

[0010] The present embodiment provides a positive electrode active material, wherein the surface of primary particles of a positive electrode matrix material is coated with a first coating layer. The lithium concentration in the first coating layer is lower than that in the positive electrode matrix material. Thus, a certain lithium concentration gradient exists between the positive electrode matrix material and the first coating layer, which facilitates the release of lithium ions from the positive electrode matrix material, thereby facilitating the increase of the active lithium ion content in the battery cell. The first coating layer and the second coating layer are sequentially coated on the surface of the primary particles of the positive electrode matrix material. That is, the outer surface of the first coating layer is coated with the second coating layer, which comprises an ion conductor material. The ion conductor material has excellent ion transport properties, resulting in high ion conductivity in the positive electrode active material and low impedance in the battery cell. The provision of the second coating layer also helps suppress side reactions between the positive electrode matrix material and the electrolyte, reducing the impedance of the solid-liquid interface at the positive electrode, thereby improving the cycling performance of the battery cell. Therefore, the positive electrode active material of the present embodiment has excellent performance and can improve the cycling performance of the battery cell.

[0011] In one possible implementation, the chemical formula of the positive electrode matrix material is Li 1+a [Ni x Co y Mn z M b ]O2, wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr, 0.6≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0≤a≤0.2, 0≤b≤0.1, x+y+z+b=1.

[0012] Battery cells made with the positive electrode matrix material of the above chemical formula have a high energy density. When the positive electrode matrix material satisfies the above chemical formula, the first coating layer facilitates the deintercalation of lithium ions from the positive electrode matrix material, while the second coating layer helps inhibit the dissolution of transition metal ions in the positive electrode matrix material, thereby achieving better performance for the positive electrode active material and the battery cells made with the positive electrode active material.

[0013] In a possible implementation, 0.8≤x<1. In this way, the content of nickel in the positive electrode matrix material is relatively high, so that the positive electrode active material has a higher gram capacity while having better stability.

[0014] In one possible implementation, M includes at least one of Ti, Nb, Te, V, or Ta. By doping the positive electrode matrix material with the M element, the crystal structure stability of the positive electrode matrix material can be improved, and the reversibility of the layered structure of the positive electrode matrix material during lithium insertion and extraction can be improved, thereby improving the electrochemical performance of the positive electrode active material. In addition, the M element can form higher-valence ions. According to defect chemistry theory, high-valence ion doping will generate lithium vacancies within the material, which is beneficial to promote the transport of lithium ions within the positive electrode matrix material.

[0015] In a possible implementation, the ion conductor material includes a compound formed by Li element and at least one of W, Mo or P element; optionally, the ion conductor material includes at least one of Li2WO4, Li2MoO4 or Li3PO4.

[0016] Due to various manufacturing factors, the surface of the positive electrode matrix material may contain stray lithium, such as lithium carbonate. W, Mo, or P elements can react with the stray lithium to form compounds composed of Li and at least one of these elements. The inclusion of these compounds in ionic conductor materials not only reduces impedance at the positive electrode interface, but also lowers the internal resistance of the battery cell. Furthermore, the inclusion of these compounds facilitates lithium ion transport, improving the rate performance of the battery cell.

[0017] In one possible implementation, the material of the first coating layer includes a transition metal oxide, wherein the transition metal in the transition metal oxide is the same as the transition metal in the positive electrode base material. In other words, the first coating layer can be formed by treating the positive electrode base material, and the lithium vacancies in the first coating layer are greater than those in the positive electrode base material, thereby facilitating the intercalation and deintercalation of lithium ions in the positive electrode base material.

[0018] In one possible implementation, the thickness d1 of the first coating layer satisfies the following conditions: 1 nm ≤ d1 ≤ 5 nm; alternatively, 1 nm ≤ d1 ≤ 2 nm. This provides a suitable transport path for lithium ions and a suitable lithium concentration gradient between the first coating layer and the positive electrode substrate, thereby facilitating improved battery cell capacity.

[0019] In one possible implementation, the thickness d2 of the second coating layer satisfies: d2≤20nm; optionally, 4nm≤d2≤10nm. In this way, lithium ions have a transmission path of appropriate length, which is beneficial to improving the capacity of the battery cell.

[0020] In one possible implementation, the ratio B of the mass of the second coating layer to the mass of the positive electrode base material satisfies: 1000ppm≤B≤3000ppm; alternatively, 1000ppm≤B≤2000ppm. In this way, the second coating layer has an appropriate mass ratio, and thus the second coating layer can have an appropriate thickness.

[0021] In one possible implementation, the volume particle size distribution of the positive electrode active material satisfies: (D v 90-D v 10) / D v 501≥1.2; Optionally, (D v 90-D v 10) / D v 501≥1.3. In this way, the positive electrode active material contains both large particles and small particles at appropriate contents, and the positive electrode active material has a wide particle size distribution, which is beneficial to improving the powder compaction density of the positive electrode active material, thereby improving the volume energy density of the battery cell.

[0022] In one possible implementation, the volume particle size distribution Dv501 of the positive electrode active material satisfies the following conditions: 7 μm ≤ Dv501 ≤ 12 μm; alternatively, 8 μm ≤ Dv501 ≤ 10 μm. This allows lithium ions to have a suitable path length when being deintercalated from the positive electrode active material, enabling the battery cell to have higher capacity and cycling performance.

[0023] In one possible implementation, the first coating layer includes a material having a spinel structure. The positive electrode base material can react with an ammonium salt, and the thermal decomposition product of the ammonium salt can react with lithium oxide (e.g., Li2O) within the positive electrode base material and residual lithium on the surface, thereby generating lithium vacancies on the surface of the positive electrode base material. The surface of the positive electrode base material transforms from a layered structure to a spinel structure, thereby generating a first coating layer including a material having a spinel structure.

[0024] In one possible implementation, the positive electrode active material is a material obtained by reacting secondary particles of the positive electrode base material with an ammonium salt. During the reaction, the ammonium salt and its decomposition products can penetrate the grain boundaries of the positive electrode base material, thereby forming a first coating layer and a second coating layer on the surface of the primary particles of the positive electrode base material.

[0025] In the second aspect, a method for preparing the positive electrode active material in the first aspect and any possible implementation thereof is provided, comprising: preparing a positive electrode base material; preparing the first coating layer and the second coating layer on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material.

[0026] In one possible implementation, the preparing the first coating layer and the second coating layer on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material includes: mixing the positive electrode base material and ammonium salt and sintering them in an inert atmosphere to obtain the positive electrode active material.

[0027] The positive electrode base material can react with the ammonium salt to form a first coating layer on the surface of the positive electrode base material. Compounds produced by the decomposition of the ammonium salt can then react with the miscellaneous lithium on the surface of the positive electrode base material, consuming the miscellaneous lithium and simultaneously forming a second coating layer. Furthermore, sintering in an inert atmosphere facilitates the formation and preparation of the first coating layer. Therefore, the positive electrode active material of the present embodiment can be prepared by the reaction of the positive electrode base material with the ammonium salt.

[0028] In one possible implementation, the mixing of the positive electrode matrix material and the ammonium salt and sintering them in an inert atmosphere to obtain the positive electrode active material includes: placing the positive electrode matrix material and the ammonium salt in a high-energy ball mill for mixing; and sintering the mixed positive electrode matrix material and the ammonium salt in an inert atmosphere to obtain the positive electrode active material.

[0029] During the ball milling and sintering process in a high-temperature ball mill, the ammonium salt melts and penetrates the grain boundaries of the cathode matrix material, allowing the ammonium salt to fully contact the surface of the primary particles of the cathode matrix material. The ball milling process facilitates the mixing of the ammonium salt and the cathode matrix material, facilitating the uniform distribution of the ammonium salt on the surface and grain boundaries of the primary particles of the cathode matrix material. During the sintering process, ammonia gas produced by the decomposition of the ammonium salt reacts with the cathode matrix material to form a spinel structure with lithium vacancies, thereby forming a first coating layer. In addition, compounds produced by the decomposition of the ammonium salt react with the stray lithium on the surface of the cathode matrix material, consuming the stray lithium and forming a second coating layer.

[0030] In a possible implementation, the rotation speed V of the high-energy ball mill satisfies: 500 rpm≤V≤1400 rpm; optionally, 800 rpm≤V≤1200 rpm.

[0031] In a possible implementation, the ball milling time t1 satisfies: 0.5h≤t1≤3h; optionally, 1h≤t1≤2h.

[0032] At the above rotation speed and / or ball milling time, the energy generated by high-energy ball milling can promote the interaction between the ammonium salt and the positive electrode matrix material, allowing the ammonium salt to enter the grain boundary gaps of the positive electrode matrix material, thereby facilitating the reaction between the ammonium salt and the positive electrode matrix material.

[0033] In a possible implementation, the sintering temperature T1 satisfies: 400°C ≤ T1 ≤ 600°C; optionally, 400°C ≤ T1 ≤ 500°C.

[0034] In a possible implementation, the sintering time t2 satisfies: 4h≤t2≤8h; optionally, 5h≤t2≤6h.

[0035] The above sintering temperature and sintering time facilitate the decomposition of the ammonium salt and the reaction of the decomposition products of the ammonium salt with the positive electrode matrix material and the miscellaneous lithium, thereby facilitating the preparation of the first coating layer and the second coating layer.

[0036] In one possible implementation, the ammonium salt includes at least one of W, Mo, or P. Alternatively, the ammonium salt includes at least one of ammonium molybdate, ammonium paramolybdate, ammonium metatungstate, ammonium phosphate, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate. W, Mo, or P reacts with the lithium in the miscellaneous lithium to form a corresponding lithium-containing compound, thereby forming the second coating layer. The ammonium salt includes W, Mo, or P and has a suitable melting point, facilitating decomposition during sintering.

[0037] In one possible implementation, the preparation of the positive electrode matrix material includes: preparing a precursor of the positive electrode matrix material; mixing the precursor, a lithium salt, and a compound containing an M element and sintering them to prepare the positive electrode matrix material, wherein the M element includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr.

[0038] By mixing and sintering a precursor, a lithium salt and a compound containing an M element, a positive electrode matrix material containing the M element can be obtained, so that the positive electrode matrix material has a higher crystal structure stability.

[0039] In one possible implementation, the molar ratio C of the lithium salt to the metal element in the precursor satisfies: 0.95≤C≤1.15; and / or the sintering temperature T2 satisfies: 650°C≤T2≤950°C; and / or the sintering time t3 satisfies: 10h≤t2≤20h.

[0040] In a possible implementation, based on the total mass of the precursor, the lithium salt, and the compound containing the element M, the mass content D of the compound containing the element M satisfies: 200 ppm≤D≤5000 ppm.

[0041] By reasonably setting the sintering temperature and time of the precursor, lithium salt and compound containing the M element, as well as the mass content of the compound containing the M element, it is beneficial to obtain a positive electrode matrix material uniformly doped with the M element.

[0042] In one possible implementation, the volume particle size distribution Dv502 of the precursor satisfies: 7 μm ≤ Dv502 ≤ 12 μm; alternatively, 8 μm ≤ Dv502 ≤ 10 μm. This is conducive to obtaining a positive electrode active material with a suitable volume particle size distribution.

[0043] In a third aspect, a positive electrode plate is provided, comprising the positive electrode active material of the first aspect and any possible implementation thereof, and / or the positive electrode active material prepared by the method of the second aspect and any possible implementation thereof.

[0044] In a fourth aspect, a battery cell is provided, comprising the positive electrode sheet described in the third aspect.

[0045] In a fifth aspect, a battery is provided, comprising the battery cell described in the fourth aspect.

[0046] In a sixth aspect, an electrical device is provided, comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0048] FIG1 is a schematic diagram of a positive electrode active material according to an embodiment of the present application;

[0049] FIG2 is a SEM image of a positive electrode active material according to an embodiment of the present application;

[0050] FIG3 is a cross-sectional view of an ion milling of a positive electrode active material according to an embodiment of the present application;

[0051] FIG4 is a schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application;

[0052] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0053] FIG6 is a schematic diagram of a battery according to an embodiment of the present application;

[0054] FIG. 7 is a schematic diagram of an electrical device according to an embodiment of the present application. DETAILED DESCRIPTION

[0055] The embodiments of the positive electrode active material and its preparation method, positive electrode sheet, battery cell, battery, and electrical device of the present application are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0056] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0057] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0058] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0059] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0060] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing active ions to pass through. In some embodiments, the above-mentioned battery cell is also called a secondary battery, and the battery cell can be the smallest battery unit.

[0061] During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, lithium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0062] It should be understood that the "embedding" process described in this application refers to the process in which lithium ions are embedded in the positive electrode active material and the negative electrode material due to electrochemical reactions, and the "extraction" and "deintercalation" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material and the negative electrode material due to electrochemical reactions.

[0063] The development of battery technology requires simultaneous consideration of multiple design factors, such as energy density, cycle life, discharge capacity, charge and discharge rate, and reliability. A battery cell includes a positive electrode plate. The performance of the positive active material in the positive electrode plate is crucial to the capacity, cycle performance, and charge and discharge rate performance of the battery cell. To improve the performance of the positive active material, a coating layer is usually placed on the surface of the positive electrode base material to improve the corresponding performance of the battery cell. However, how to place the coating layer and what type of coating layer to place to improve the performance of the battery cell is a technical problem that needs to be solved urgently.

[0064] In view of this, an embodiment of the present application provides a positive electrode active material, including a positive electrode base material, and a first coating layer and a second coating layer sequentially coated on the surface of primary particles of the positive electrode base material, wherein the concentration of lithium element in the first coating layer is less than the concentration of lithium element in the positive electrode base material, and the second coating layer includes an ion conductor material, which is beneficial to improving the cycle performance of the battery cell.

[0065] [Positive electrode active material]

[0066] FIG1 is a schematic diagram of a positive electrode active material according to an embodiment of the present application. This embodiment of the present application provides a positive electrode active material 1. As shown in FIG1 , the positive electrode active material 1 comprises a positive electrode base material 10, and a first coating layer 11 and a second coating layer 12 sequentially coated on the surface of primary particles of the positive electrode base material 10.

[0067] The positive electrode matrix material 10 can be a layered transition metal oxide, such as a ternary material or a lithium-rich manganese-based material. During the charge and discharge process of the battery cell, the active lithium ions in the positive electrode matrix material 10 can be released from or embedded in the positive electrode matrix material 10. In other words, the positive electrode matrix material 10 can be a material that provides active lithium ions.

[0068] In FIG1 , the positive electrode base material indicates the positive electrode base material of primary particles.

[0069] Primary particles refer to unagglomerated particles, while secondary particles refer to particles formed by agglomeration of primary particles. In other words, a primary particle is a single unagglomerated particle. Positive electrode active materials are prepared from precursors of the positive electrode matrix material. For example, in the case of ternary materials, during the precursor preparation process, Ni, Co, and Mn metal ions react to form primary particles. These primary particles aggregate or agglomerate to form a nearly spherical precursor, which becomes the agglomerated secondary particle.

[0070] Figure 2 is a SEM image of the positive electrode active material according to one embodiment of the present application, and Figure 3 is a cross-sectional view of the positive electrode active material according to one embodiment of the present application after ion milling. As shown in Figures 2 and 3, the large spherical particles in the SEM image are secondary particles, each of which contains multiple primary particles. In the cross-sectional view of the ion milling, it can be seen that the secondary particles contain multiple primary particles. Furthermore, as shown in Figure 1, the surfaces of the primary particles in the positive electrode active material according to one embodiment of the present application are provided with a first coating layer 11 and a second coating layer 12.

[0071] The first coating layer 11 and the second coating layer 12 are sequentially coated on the surface of the primary particles of the positive electrode base material 10. In other words, in the primary particles of the positive electrode active material 1, from the outside to the inside, there are the second coating layer 12, the first coating layer 11 and the positive electrode base material 10.

[0072] In the case where a coating layer is provided on the surface of the secondary particles of the positive electrode matrix material 10, the secondary particles of the positive electrode active material 1 include secondary particles (formed by the agglomeration of multiple primary particles of the positive electrode matrix material) and a coating layer that coats the entire secondary particles. In this case, after the secondary particles crack, at least part of the surface of the positive electrode matrix material is not provided with a coating layer, and the surface of the positive electrode matrix material contacts the electrolyte in the battery cell. Side reactions are more likely to occur at the positive electrode interface, which is not conducive to improving the performance of the battery cell. Compared to providing a coating layer on the surface of the secondary particles of the positive electrode matrix material 10, in the arrangement of the embodiment of the present application, the surface of the primary particles of the positive electrode active material 1 is provided with a first coating layer 11 and a second coating layer 12. Even after the secondary particles crack, the positive electrode matrix material 10 will not contact the electrolyte or the risk of contacting the electrolyte is greatly reduced, thereby suppressing side reactions at the positive electrode interface, which is beneficial to reducing the impedance of the battery cell and improving the cycle performance of the battery cell.

[0073] The concentration of lithium in the first coating layer is lower than that in the positive electrode base material. Thus, a certain lithium concentration gradient exists between the positive electrode base material 10 and the first coating layer 11, which facilitates the release of lithium ions from the positive electrode base material 10, thereby increasing the content of active lithium ions in the battery cell and, in turn, the capacity of the battery cell.

[0074] The second cladding layer 12 includes an ion conductor material.

[0075] An ionic conductor is one in which current is generated by mobile ionic charges. Unlike conductors and semiconductors, its charge carriers are neither electrons nor holes, but rather mobile ions. The ionic conductor material in the embodiments of this application may refer to a fast ion conductor material, which refers to a material with a high ion mobility that can rapidly transport ions.

[0076] The ion conductor material can be a compound formed by an oxide of one or more elements selected from the group consisting of Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, Bi, P, B, Si, N, and S and lithium, or a mixture of its oxides and compounds, for example, Li3PO4.

[0077] Ionic conductor materials have excellent ion transport properties, which helps increase the lithium ion transmission rate and improve the rate performance of the battery cell. In addition, the second coating layer 12 can also reduce the risk of direct contact between the positive electrode base material 10 and the electrolyte, which helps to inhibit side reactions between the positive electrode base material 10 and the electrolyte, and reduce the impedance of the solid-liquid interface at the positive electrode, thereby improving the cycle performance of the battery cell.

[0078] The embodiment of the present application provides a positive electrode active material 1, wherein the surface of the primary particles of the positive electrode base material 10 is coated with a first coating layer 11. The concentration of lithium in the first coating layer 11 is lower than the concentration of lithium in the positive electrode base material 10. Thus, a certain lithium concentration gradient exists between the positive electrode base material 10 and the first coating layer 11, which is conducive to the release of lithium ions in the positive electrode base material 10 from the positive electrode base material 10, thereby facilitating the increase of the content of active lithium ions in the battery cell, thereby increasing the capacity of the battery cell. The first coating layer 11 and the second coating layer 12 are sequentially coated on the surface of the particles of the positive electrode base material 10, that is, the outer surface of the first coating layer 11 is coated with the second coating layer 12, and the second coating layer 12 comprises an ion conductor material. Ionic conductor materials have excellent ion transport properties, which helps increase the lithium ion transmission rate and improve the rate performance of the battery cell. The second coating layer 12 also helps suppress side reactions between the positive electrode matrix material 10 and the electrolyte, reducing the impedance of the solid-liquid interface at the positive electrode, thereby improving the cycle performance of the battery cell. Therefore, the positive electrode active material 1 of the embodiment of the present application has excellent performance and can improve the performance of the battery cell.

[0079] In some embodiments, the chemical formula of the positive electrode matrix material 10 is Li 1+a [Ni x Co y Mn z M b ]O2, wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr, 0.6≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0≤a≤0.2, 0≤b≤0.1, x+y+z+b=1.

[0080] x can be 0.6, 0.7, 0.8, 0.9 or any value within the above range, y can be 0.1, 0.2, 0.3, 0.4 or any value within the above range, z can be 0.1, 0.2, 0.3, 0.4 or any value within the above range, b can be 0, 0.1 or any value within the above range, and a can be 0, 0.1, 0.2 or any value within the above range.

[0081] When x is greater than or equal to 0.6, the nickel content in the positive electrode base material is higher. Compared with positive electrode base materials with lower nickel content (e.g., materials with x less than 0.6), this high-nickel positive electrode base material is more unstable in structure and more prone to side reactions. Providing the first coating layer 11 and the second coating layer 12 on the primary particles of this high-nickel positive electrode base material is beneficial for improving the performance of the positive electrode active material 1, thereby enhancing the cycle performance and rate performance of the battery cell while ensuring a higher energy density.

[0082] In addition, for the positive electrode matrix material with x greater than or equal to 0.6, the prepared positive electrode matrix material is mostly in the morphology of secondary particles. During the use of the battery cell, the secondary particles are prone to cracking. Therefore, it is more necessary to set the first coating layer and the second coating layer for the primary particles of the positive electrode matrix material with x greater than or equal to 0.6.

[0083] M can be a doping element. When b is 0, the positive electrode matrix material 10 can be a ternary material. For example, the positive electrode matrix material 10 is LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.; in the case where b is greater than 0, the positive electrode base material 10 can be LiNi 0.6 Co 0.2 Mn 0.1 Al 0.1 O2.

[0084] In some embodiments, the M element is uniformly or relatively uniformly doped in the positive electrode matrix material 10, which helps to make the performance of the positive electrode matrix material more stable. The uniform doping of the M element can be tested by EDS, for example, by observing whether the content of the M element in different regions is roughly the same to determine whether the M element is uniformly doped.

[0085] Optionally, the positive electrode matrix material 10 having the above chemical formula may be doped with elements such as F, S, P, N, and B, and these elements may occupy the position of O.

[0086] It should be noted that the battery cell will be accompanied by the deintercalation and consumption of Li during the charge and discharge process. The molar content of Li is different when the battery is discharged to different states. The above definition of a includes the molar content of Li under different charge and discharge states of the battery (usually the battery voltage is between 2-5V). In the enumeration of positive electrode matrix materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode matrix material is applied to the battery system, and after the charge and discharge cycle, the molar content of Li will change. In the enumeration of positive electrode matrix materials in this application, the molar content of O is only a theoretical state value. Lattice oxygen release will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0087] In this embodiment, the battery cell prepared from the positive electrode matrix material 10 of the above chemical formula has a high energy density. When the positive electrode matrix material 10 satisfies the above chemical formula, the first coating layer 11 facilitates the deintercalation of lithium ions from the positive electrode matrix material 10; the second coating layer 12 facilitates the suppression of the dissolution of transition metal ions in the positive electrode matrix material 10 and side reactions between the positive electrode matrix material 10 and the electrolyte. As a result, the positive electrode active material 1 has good crystal structure stability, retains a high level of active ions, and has good storage performance, thereby achieving higher cycle stability and capacity of the battery cell.

[0088] In some embodiments, 0.8≤x<1. For example, x is 0.9175. Thus, the nickel content in the positive electrode matrix material 10 is relatively high, so that the positive electrode active material 1 has a higher gram capacity while having better stability.

[0089] In some embodiments, 0≤x<0.6, for example, the positive electrode matrix material 10 is LiNi 0.3 Co 0.4 Mn 0.3 That is to say, the positive electrode base material 10 can also be a material with a slightly lower nickel content.

[0090] In some embodiments, M includes at least one of Ti, Nb, Te, V, or Ta.

[0091] By doping the positive electrode matrix material 10 with the M element, the crystal structure stability of the positive electrode matrix material 10 can be improved, and the reversibility of the layered structure of the positive electrode matrix material 10 during lithium insertion and removal can be increased, thereby enhancing the electrochemical performance of the positive electrode active material 1. In addition, the M element can form higher-valence ions. According to defect chemistry theory, high-valence ion doping will generate lithium vacancies within the material, thereby promoting the transport of lithium ions within the positive electrode matrix material 10.

[0092] In some embodiments, the ion conductor material includes a compound formed by Li element and at least one of W, Mo, or P element.

[0093] Due to various reasons, such as preparation, the surface of the positive electrode substrate 10 may contain stray lithium (also known as residual lithium), such as lithium carbonate. W, Mo, or P elements can react with the stray lithium to form a compound composed of Li and at least one of W, Mo, or P. This not only consumes the stray lithium but also generates the corresponding compound. The resulting compound has excellent ion transport and conductivity, which helps improve the rate performance of the battery cell and reduce the internal resistance of the battery cell.

[0094] Optionally, the ion conductor material includes at least one of Li2WO4, Li2MoO4, or Li3PO4. The inclusion of these compounds in the ion conductor material can, on the one hand, reduce the impedance at the positive electrode interface and thus the internal resistance of the battery cell; and, on the other hand, facilitate lithium ion transport and improve the rate performance of the battery cell.

[0095] In some embodiments, the material of the first coating layer 11 includes a transition metal oxide, and the transition metal in the transition metal oxide is the same as the transition metal in the positive electrode base material 10. In other words, the first coating layer 11 can be formed by subjecting the positive electrode base material 10 to certain treatments, and the lithium vacancies in the first coating layer 11 are greater than those in the positive electrode base material 10, thereby facilitating the intercalation and deintercalation of lithium ions in the positive electrode base material 10.

[0096] In some embodiments, the thickness d1 of the first cladding layer 11 satisfies: 1 nm≤d1≤5 nm.

[0097] d1 can be 1 nm, 2 nm, 3 nm, 5 nm or any value within the above range.

[0098] When d1 is not less than 1 nm, there is a suitable lithium concentration gradient between the first coating layer 11 and the positive electrode matrix material 10, which facilitates the deintercalation of lithium ions from the positive electrode matrix material 10; when d1 does not exceed 5 nm, lithium ions have a transmission path of suitable length.

[0099] In this way, by setting 1nm≤d1≤5nm, lithium ions have a transmission path of appropriate length, and there is an appropriate lithium concentration gradient between the first coating layer 11 and the positive electrode base material 10, which is beneficial to improving the capacity of the battery cell.

[0100] Optionally, 1nm≤d1≤2nm. In this way, the battery cell has a higher rate performance.

[0101] In some embodiments, the thickness d2 of the second cladding layer 12 satisfies: d2≤20 nm.

[0102] d2 can be 1 nm, 2 nm, 3 nm, 5 nm, 10 nm, 15 nm, 20 nm or any value within the above range.

[0103] When d2 does not exceed 20nm, lithium ions have a transmission path of appropriate length, which is beneficial to improving the capacity of the battery cell.

[0104] When d2 is not less than 1 nm, the second coating layer 12 can play a certain protective role, inhibiting the side reaction between the positive electrode base material 10 and the electrolyte, which is beneficial to improving the cycle performance of the battery cell.

[0105] Optionally, 4nm≤d2≤10nm, and the battery cell has both higher capacity and cycle performance.

[0106] In some embodiments, based on the total mass of the positive electrode active material 1 , the mass content B of the second coating layer 12 satisfies: 1000 ppm≤B≤3000 ppm; alternatively, 1000 ppm≤B≤2000 ppm.

[0107] B can be 1000 ppm, 1500 ppm, 2000 ppm, 3000 ppm or any value within the above range.

[0108] In this way, the second cladding layer 12 has an appropriate mass ratio, so that the second cladding layer 12 can have an appropriate thickness.

[0109] In some embodiments, the volume particle size distribution of the positive electrode active material 1 satisfies: (D v 901-D v 101) / D v 501≥1.2; Optionally, (D v 901-D v 101) / D v 501≥1.3.

[0110] D v 10 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 10%, or it can refer to the particle size smaller than it accounting for 10%.

[0111] D v 50 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 50%, or it can refer to the particle size smaller than it accounting for 50%. v 501 is to match the D below v 502 is used to distinguish and represent the volume average particle size of different materials.

[0112] D v 90 can refer to the particle size corresponding to when the cumulative particle size volume distribution number of a sample reaches 90%, or it can refer to the particle size smaller than it accounting for 90%. v 901, D v 101 is used to represent the D of the positive electrode active material 1 v 90.D v 10.

[0113] In this way, the positive electrode active material 1 contains both large particles and small particles at appropriate contents. The positive electrode active material 1 has a wider distribution of particle sizes, which is beneficial to improving the powder compaction density of the positive electrode active material 1, thereby helping to improve the volume energy density of the battery cell.

[0114] In some embodiments, the volume particle size distribution Dv501 of the positive electrode active material 1 satisfies the following conditions: 7 μm ≤ Dv501 ≤ 12 μm; alternatively, 8 μm ≤ Dv501 ≤ 10 μm. This allows lithium ions to have a suitable path length when being intercalated and deintercalated from the positive electrode active material 1, resulting in a battery cell with higher capacity and cycle performance.

[0115] It should be noted that Dv501 and Dv502 in the examples of this application both represent the volume average particle size of the material, wherein the "1" in Dv501 and the "2" in Dv502 are used to distinguish the volume average particle size of different materials. Similarly, the "1" in Dv901 and Dv101 and the "2" in Dv502 are used to distinguish the volume average particle size of different materials.

[0116] In some embodiments, the positive electrode active material 1 is a material obtained by reacting secondary particles of the positive electrode base material 10 with an ammonium salt. During the reaction, the ammonium salt and its decomposition products can penetrate the grain boundaries of the positive electrode base material 10, thereby forming a first coating layer 11 and a second coating layer 12 on the surface of the primary particles of the positive electrode base material 10.

[0117] In some embodiments, the first coating layer 11 includes a spinel structured material having lithium vacancies.

[0118] Spinel structure refers to the crystal structure of a material. Materials with a spinel structure have three-dimensional lithium ion transmission channels, which helps to increase the transmission rate of lithium ions and thus improve the rate performance of battery cells.

[0119] The positive electrode base material 10 can react with an ammonium salt. The thermal decomposition product of the ammonium salt can react with the lithium oxide (e.g., Li2O) in the positive electrode base material 10 and the residual lithium on the surface, thereby generating lithium vacancies on the surface of the positive electrode base material. The surface of the positive electrode base material transforms from a layered structure to a spinel structure, thereby generating a first coating layer comprising a material having a spinel structure. Taking ammonium tungstate as an example, the generation of lithium vacancies is as follows: ammonium tungstate decomposes upon thermal decomposition to produce NH3 and WO3. NH3 and WO3 react with the surface of the positive electrode base material 10. WO3 reacts with the Li2O in the lattice of the surface layer of the positive electrode base material and the residual lithium on the surface, causing lithium vacancies to be generated on the surface of the positive electrode base material. The structure then transforms from a layered structure to a spinel structure, generating a first coating layer of a spinel phase and a second coating layer of Li2WO3.

[0120] The positive electrode active material is described above in conjunction with Figures 1-3. The preparation method of the positive electrode active material will be described below in conjunction with Figure 4. Parts of the preparation method corresponding to or similar to the product of the positive electrode active material can be found in the above description and will not be repeated here.

[0121] [Method for preparing positive electrode active material]

[0122] Figure 4 is a schematic diagram of a method for preparing a positive electrode active material according to one embodiment of the present application. As shown in Figure 4 , this embodiment of the present application provides a method 200 for preparing a positive electrode active material, comprising the following steps. Method 200 can be used to prepare the positive electrode active material 1 described in any of the above embodiments.

[0123] Step 210 , preparing the positive electrode base material 10 .

[0124] The positive electrode matrix material 10 may be a layered lithium-containing transition metal oxide, such as a ternary material.

[0125] In step 220 , a first coating layer 11 and a second coating layer 12 are formed on the surface of the primary particles of the positive electrode base material 10 to obtain a positive electrode active material.

[0126] For example, in step 220 , the first coating layer 11 is obtained by acid etching and sintering, and then the second coating layer 12 is obtained by mixing with an ion conductor material and sintering.

[0127] In some embodiments, step 220 includes: mixing the positive electrode base material 10 and the ammonium salt and sintering the mixture in an inert atmosphere to obtain the positive electrode active material 1 .

[0128] The inert atmosphere can be a nitrogen atmosphere or an argon atmosphere. Sintering in an inert atmosphere facilitates the formation of the first coating layer 11 .

[0129] The positive electrode base material 10 can react with the ammonium salt, thereby forming a first coating layer 11 on the surface of the positive electrode base material 10. The compound produced by the decomposition of the ammonium salt can react with the miscellaneous lithium on the surface of the positive electrode base material 10, consuming the miscellaneous lithium and forming a second coating layer 12. Therefore, the positive electrode active material 1 of the embodiment of the present application can be prepared by the reaction between the positive electrode base material 10 and the ammonium salt. In addition, this method is relatively simple and can form the first coating layer 11 and the second coating layer 12 with a relatively small number of sintering times.

[0130] In some embodiments, the positive electrode base material 10 and the ammonium salt are mixed and sintered in an inert atmosphere to obtain the positive electrode active material 1, including: placing the positive electrode base material 10 and the ammonium salt in a high-energy ball mill for mixing; placing the mixed positive electrode base material 10 and the ammonium salt in an inert atmosphere and sintering to obtain the positive electrode active material 1.

[0131] During the ball milling and sintering process in a high-temperature ball mill, the ammonium salt can melt and penetrate the grain boundaries of the positive electrode matrix material 10, thereby allowing the ammonium salt to fully contact the surface of the primary particles of the positive electrode matrix material 10. The ball milling process facilitates the mixing of the ammonium salt and the positive electrode matrix material 10, and facilitates the uniform distribution of the ammonium salt on the surface and grain boundaries of the primary particles of the positive electrode matrix material 10. During the sintering process, ammonia produced by the decomposition of the ammonium salt reacts with the positive electrode matrix material 10 to form a material with a spinel structure having lithium vacancies, thereby forming the first coating layer 11. In addition, the compound produced by the decomposition of the ammonium salt reacts with the miscellaneous lithium on the surface of the positive electrode matrix material 10, consuming the miscellaneous lithium and forming the second coating layer 12.

[0132] In some embodiments, the rotation speed V of the high energy ball mill satisfies: 500 rpm≤V≤1400 rpm; optionally, 800 rpm≤V≤1200 rpm.

[0133] V can be 500 rpm, 600 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1400 rpm or any value within the above range.

[0134] In some embodiments, the ball milling time t1 satisfies: 0.5h≤t1≤3h; optionally, 1h≤t1≤2h.

[0135] t1 can be 0.5h, 1h, 2h, 3h or any value within the above range.

[0136] At the above rotation speed and / or ball milling time, the energy generated by high-energy ball milling can promote the interaction between the ammonium salt and the positive electrode matrix material 10, allowing the ammonium salt to enter the grain boundary gaps of the positive electrode matrix material 10, thereby facilitating the reaction between the ammonium salt and the positive electrode matrix material 10.

[0137] In some embodiments, the sintering temperature T1 satisfies: 400°C≤T1≤600°C; optionally, 400°C≤T1≤500°C.

[0138] T1 can be 400°C, 500°C, 600°C or any value within the above range.

[0139] When the temperature T1 is not less than 400°C, the risk of the positive electrode matrix material 10 being difficult to react with the ammonium salt due to too low a temperature can be reduced; when the temperature T1 is not greater than 600°C, the risk of more oxygen vacancies being formed inside the positive electrode matrix material 10 due to too high a temperature can be reduced, thereby reducing the risk of deterioration in the performance of the positive electrode active material 1 and the performance of the battery cell.

[0140] In some embodiments, the sintering time t2 satisfies: 4h≤t2≤8h; optionally, 5h≤t2≤6h.

[0141] t2 can be 4h, 5h, 6h, 8h, 10h or any value within the above range.

[0142] When the time t1 is not less than 4 hours, the risk of insufficient reaction between the positive electrode matrix material 10 and the ammonium salt due to too short a time can be reduced; when the time t1 is not greater than 6 hours, the risk of more oxygen vacancies forming inside the positive electrode matrix material 10 due to too long a time can be reduced.

[0143] The above sintering temperature and sintering time facilitate the decomposition of the ammonium salt and the reaction of the decomposition products of the ammonium salt with the positive electrode base material 10 and the miscellaneous lithium, thereby facilitating the preparation of the first coating layer 11 and the second coating layer 12 .

[0144] In some embodiments, the ammonium salt includes at least one of W, Mo, or P. The W, Mo, or P element can react with the lithium element in the miscellaneous lithium to generate a corresponding lithium-containing compound, thereby forming the second coating layer 12 .

[0145] In some embodiments, the ammonium salt includes at least one of ammonium molybdate, ammonium paramolybdate, ammonium metatungstate, ammonium phosphate, ammonium hydrogen phosphate, or ammonium dihydrogen phosphate. The ammonium salt includes W, Mo, or P and has a suitable melting point to facilitate decomposition during sintering.

[0146] In some embodiments, step 210 includes: preparing a precursor of the positive electrode matrix material 10; mixing the precursor, a lithium salt, and a compound containing an M element and sintering them to prepare the positive electrode matrix material 10, where the M element includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta, or Sr.

[0147] As an example, the positive electrode base material 10 is a ternary material, and the chemical formula of the precursor of the positive electrode base material 10 is [Ni x Co y Mn z ](OH)2, wherein 0.6≤x≤1, 0≤y≤0.4, 0≤z≤0.4. Optionally, 0.8≤x<1.

[0148] The precursor, lithium salt, and compound containing element M can be sintered in air or an O2 atmosphere, and the lithium salt can be at least one of lithium carbonate and lithium hydroxide.

[0149] As an example, the mixing can be specifically performed by the following operation: the precursor, the lithium salt and the compound containing the M element are added into a plowshare mixer, a high-speed mixer or an inclined mixer in a certain proportion for mixing, and then sintered in an air atmosphere.

[0150] As an example, the positive electrode matrix material 10 is a ternary material, and the precursor of the positive electrode matrix material 10 can be prepared by the following steps. (1) Synthesizing seed crystals: according to the molar ratio of nickel, cobalt and manganese in the ternary material, a mixed metal solution of nickel salt, cobalt salt and manganese salt with a concentration of 0.5 to 2.5 mol / L is prepared; a 1 to 10 mol / L NaOH alkaline solution is prepared; an ammonia solution with a concentration of 2 to 14 mol / L is prepared; 10% to 50% pure water is added to a 100 L reactor, stirring is started, and a constant temperature of 40 to 75 ° C is maintained; a certain amount of NaOH solution is added to a pH of 11.5 to 12.5, optionally 11.8 to 12.2; a certain amount of ammonia solution is added to an ammonia concentration of 0.2 to 0.6 mol / L, optionally 0.3 to 0.5 mol / L. The nickel-cobalt-manganese mixed metal solution, NaOH alkaline solution and ammonia solution were added to the reactor at a certain flow rate, and the ammonia concentration and pH in the reactor were kept constant. The volume particle size distribution D was synthesized by continuous reaction. v 50 is a seed slurry product of 1 to 5 μm. (2) Synthesis of precursor: Add 10% to 50% pure water to a 100L reactor, add 1 to 20 kg of the seed core slurry synthesized in step (1), start stirring, maintain a constant temperature of 40 to 75 ° C, add NaOH solution to a pH of 11.0 to 12.0, optionally 11.1 to 11.7, add a certain amount of ammonia solution to an ammonia concentration of 0.2 to 0.6 mol / L, optionally 0.3 to 0.5 mol / L. Add the nickel-cobalt-manganese mixed metal solution, NaOH alkaline solution and ammonia solution and the seed slurry synthesized in step (1) to the reactor at a certain flow rate, keep the ammonia concentration and pH in the reactor unchanged, and continuously react to synthesize a slurry product with a certain volume particle size distribution. The product slurry is then centrifuged, washed, filtered, and dried to obtain a precursor.

[0151] In this embodiment, the positive electrode base material 10 containing the M element can be obtained by mixing and sintering the precursor, the lithium salt, and the compound containing the M element, so that the positive electrode base material 10 has a high crystal structure stability.

[0152] In some embodiments, the molar ratio C of the lithium salt to the metal element in the precursor satisfies: 0.95≤C≤1.15; and / or, the sintering temperature T2 satisfies: 650°C≤T2≤950°C; and / or, the sintering time t3 satisfies: 10h≤t2≤20h.

[0153] The metal elements in the precursor include nickel, cobalt and manganese, and C is the ratio of the molar number of lithium salt to the total molar number of nickel, cobalt and manganese elements.

[0154] C can be 0.95, 1, 1.15, or any value within the above range. T2 can be 650°C, 800°C, 950°C, or any value within the above range. t3 can be 10h, 15h, 20h, or any value within the above range.

[0155] In some embodiments, the mass content D of the compound containing the element M, based on the total mass of the precursor, the lithium salt, and the compound containing the element M, satisfies the following conditions: 200 ppm ≤ D ≤ 5000 ppm. For example, D is 200 ppm, 1000 ppm, 3000 ppm, 5000 ppm, or any value within the foregoing range.

[0156] By properly setting the sintering temperature and time of the precursor, lithium salt, and compound containing element M, as well as the mass content of the compound containing element M, it is advantageous to obtain a positive electrode matrix material 10 uniformly doped with element M. The positive electrode matrix material 10 uniformly doped with element M has higher stability.

[0157] In some embodiments, the volume particle size distribution Dv502 of the precursor satisfies: 7 μm ≤ Dv502 ≤ 12 μm; alternatively, 8 μm ≤ Dv502 ≤ 10 μm. This is conducive to obtaining a positive electrode active material 1 with a suitable volume particle size distribution.

[0158] Dv502 can be 7 μm, 8 μm, 10 μm, 12 μm or any value within the above range.

[0159] [Positive electrode]

[0160] An embodiment of the present application provides a positive electrode plate, comprising the positive electrode active material of any of the above embodiments, and / or the positive electrode active material prepared by the preparation method of any of the above embodiments.

[0161] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0162] The positive electrode current collector may be a metal foil or a composite current collector. For example, the positive electrode current collector may be an aluminum foil.

[0163] The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as a substrate made of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0164] The positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0165] The positive electrode film layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0166] [Negative electrode]

[0167] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

[0168] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0169] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be a negative electrode active material for batteries that is well known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0170] The negative electrode film layer may further optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0171] [Electrolytes]

[0172] The electrolyte conducts ions between the positive and negative electrodes. The present invention does not specifically limit the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0173] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0174] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0175] The solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0176] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include performance additives that can improve certain battery properties, such as improving battery overcharge performance, improving battery high or low temperature performance, etc.

[0177] [Isolator]

[0178] The separator is used to separate the positive electrode sheet from the negative electrode sheet. The embodiment of the present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical and mechanical stability can be selected.

[0179] The separator can be made of at least one of fiberglass, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. In the case of a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0180] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0181] [Battery Cell]

[0182] An embodiment of the present application provides a battery cell, comprising the positive electrode sheet in the above embodiment.

[0183] The embodiment of the present application has no particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other shape. The battery cell can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, or the like.

[0184] FIG5 is a schematic diagram of a battery cell according to an embodiment of the present application. As shown in FIG5 , the battery cell 3 includes a housing 31 , an end cap assembly 32 , and an electrode assembly 33 . The electrode assembly 33 is disposed in the housing 31 , and the end cap assembly 32 is used to cover the housing 31 .

[0185] The end cap assembly 32 includes an electrode terminal 322 . For example, as shown in FIG. 5 , the end cap assembly 32 includes two electrode terminals 322 , one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0186] The electrode assembly 33 includes an electrode assembly body 331 and a tab 332 extending from the electrode assembly body 331 . The electrode assembly 33 can be made of a positive electrode sheet, a negative electrode sheet, and a separator through a winding process or a lamination process.

[0187] The battery cell 3 further includes a current collecting member 34, which is used to connect the tab 332 of the electrode assembly 33 and the electrode terminal 322. For example, as shown in FIG3 , the battery cell 3 includes two current collecting members 34, one current collecting member 34 for connecting the positive electrode tab and the positive electrode terminal, and the other current collecting member 34 for connecting the negative electrode tab and the negative electrode terminal.

[0188] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in a battery module may be one or more. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0189] [Battery]

[0190] The present invention provides a battery comprising the battery cells of the above-mentioned embodiment. FIG6 is a schematic diagram of a battery according to an embodiment of the present invention. As shown in FIG6 , the battery 5 may comprise a plurality of battery cells (not shown in the figure).

[0191] The battery cells 3 can be directly assembled into the battery 5 , or they can be assembled into battery modules first, and then multiple battery modules can be assembled into the battery 5 .

[0192] [Electrical devices]

[0193] An embodiment of the present application provides an electrical device, comprising the battery described in the above embodiment.

[0194] Figure 7 is a schematic diagram of an electric device according to an embodiment of the present application. As shown in Figure 7 , the present application provides an electric device 6 including the battery according to the above embodiment.

[0195] Optionally, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., and the embodiments of the present application include but are not limited to the above.

[0196] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0197] [Example]

[0198] Example 1

[0199] The positive electrode active material in Example 1 was prepared by the following steps.

[0200] (1) Synthesis of precursors for positive electrode matrix materials

[0201] In the precursor of the positive electrode matrix material, the molar ratio of the three elements of nickel, cobalt and manganese is 92:7:1, the volume particle size distribution Dv502 of the precursor is 8.5μm, and the volume particle size distribution (D v 902-D v 102) / D v 502 is 1.35.

[0202] (2) Synthesis of positive electrode active materials

[0203] S1: Lithium salt, Nb2O5, ZrO2 and the above precursors are mixed in a plow mixer in a certain proportion. The Li / Me molar ratio is 1.05 (Me is the total molar number of the three elements of nickel, cobalt and manganese), the Nb doping amount is 500ppm, and the Zr doping amount is 2000ppm. The mixed material is placed in a kiln for sintering. The sintering temperature T2 is 750℃, the sintering time t3 is 20h, and the sintering atmosphere is O2. The positive electrode matrix material uniformly doped with Nb and Zr is obtained by sintering. Among them, the doping amount of Nb and Zr is the doping amount of Nb element and Zr element based on the total weight of the positive electrode matrix material.

[0204] S2: The positive electrode matrix material and ammonium molybdate are placed in a high-energy ball mill for mixing. The ball milling speed V is 1000 rpm and the ball milling time t1 is 2 hours. The amount of Mo element added is 2000 ppm. The mixed material is placed in a kiln for sintering. The sintering temperature T1 is 400°C, the sintering time t2 is 6 hours, and the sintering atmosphere is N2. The primary particles of positive electrode active material are sintered. The first coating layer includes a spinel structure material with lithium vacancies, and the second coating layer includes Li2MoO4. The doping amount of Mo element is based on the total weight of the positive electrode matrix material.

[0205] In Example 1, the positive electrode matrix material is LiNi 0.92 Co 0.07 Mn0.01 O2, the thickness d1 of the first coating layer is 2 nm, the thickness d2 of the second coating layer is 6 nm, and the mass content B of the second coating layer is 2000 ppm. The volume particle size distribution Dv501 of the positive electrode active material is 8.7 μm, (D v 901-D v 101) / D v 501 is 1.35.

[0206] Example 2

[0207] The difference between Example 2 and Example 1 is that the amount of Mo added is 1000 ppm. Accordingly, in the prepared positive electrode active material, the thickness d2 of the second coating layer is 4 nm.

[0208] Example 3

[0209] The difference between Example 3 and Example 1 is that in step S2, the amount of Mo element added is 3000 ppm.

[0210] In the prepared positive electrode active material, the thickness d2 of the second coating layer was 9 nm, and the mass content B of the second coating layer was 3000 ppm.

[0211] Example 4

[0212] The difference between Example 4 and Example 1 is that the amount of Mo added is 5000 ppm. Accordingly, in the prepared positive electrode active material, the thickness d1 of the first coating layer is 5 nm, and the thickness d2 of the second coating layer is 20 nm.

[0213] Example 5

[0214] The difference between Example 5 and Example 1 is that in step S2, the ammonium salt is ammonium metatungstate and the sintering temperature T1 is 500°C.

[0215] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 5 nm, the mass content B of the second coating layer is 2000 ppm, and the second coating layer includes Li2WO4.

[0216] Example 6

[0217] The difference between Example 6 and Example 1 is that in step S2, the ammonium salt is ammonium phosphate, the amount of element P added is 2500 ppm, and accordingly, the sintering temperature T1 is 400°C.

[0218] In the prepared positive electrode active material, the thickness d2 of the second coating layer was 4.5 nm, the mass content B of the second coating layer was 2500 ppm, and the second coating layer included Li3PO4.

[0219] Example 7

[0220] The difference between Example 7 and Example 1 is that in step S2, ammonium metatungstate is additionally added, and the amount of W element added is 1000 ppm. Accordingly, the sintering temperature T1 is 450°C.

[0221] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 10 nm, the mass content B of the second coating layer is 3000 ppm, and the second coating layer includes Li2MoO4 and Li2WO4.

[0222] Example 8

[0223] The difference between Example 8 and Example 1 is that in step S2, the ammonium salts are ammonium molybdate and ammonium dihydrogen phosphate, the amount of Mo added is 1000 ppm, and the amount of P added is 1000 ppm. Accordingly, the sintering temperature T1 is 450°C.

[0224] In the prepared positive electrode active material, the thickness d2 of the second coating layer is 8.5 nm, the mass content B of the second coating layer is 3000 ppm, and the second coating layer includes Li2MoO4 and Li3PO4.

[0225] Examples 9-10

[0226] The difference between Examples 9-10 and Example 1 is that the volume particle size distribution (D v 901-D v 101) / D v 501 is different.

[0227] In Examples 1-10, the positive electrode matrix materials are the same. In the process of preparing the positive electrode active material, the sintering time t2 is 6 hours, the ball milling speed is 1000 rpm, and the ball milling time t1 is 2 hours.

[0228] Example 11

[0229] The difference between Example 11 and Example 1 is that Nb2O5 in step S1 is replaced by Ta2O5, and the doping amount of Ta is 500ppm.

[0230] Example 12

[0231] The difference between Example 12 and Example 1 is that ZrO2 in step S1 is replaced by TiO2, and the doping amount of Ti is 1000ppm.

[0232] Example 13

[0233] The difference between Example 13 and Example 1 is that SrCO3 is added in step S1, the Sr doping amount is 1000 ppm, and the sintering temperature T2 is 730°C.

[0234] Example 14

[0235] The difference between Example 14 and Example 1 is that Nb2O5 and ZrO2 are not added in step S1.

[0236] Example 15

[0237] The difference between Example 15 and Example 1 is that Nb2O5 in step S1 is replaced with TiO2, and the doping amount of Ti is 750 ppm. Ammonium molybdate in step S2 is replaced with ammonium phosphate, and the added amount of P element is 2500 ppm.

[0238] In Examples 11-15, the positive electrode matrix materials are different; in the preparation process of the positive electrode active material, the sintering temperature T1 is 400°C, the sintering time t2 is 6h, the ball milling speed is 1000rpm, and the ball milling time t1 is 2h; the positive electrode active material (D v 901-D v 101) / D v Same as 501.

[0239] Examples 16-19

[0240] The difference between Examples 16-19 and Example 1 is that the volume average particle size Dv501 of the positive electrode active material is different.

[0241] Examples 20-21

[0242] The difference between Example 20-21 and Example 1 is that the reaction temperature and time of the ammonium salt and the precursor are different.

[0243] Comparative Example 1

[0244] The difference between Comparative Example 1 and Example 1 is that the positive electrode active material in Comparative Example 1 is a positive electrode matrix material and does not include a coating layer.

[0245] Comparative Example 2

[0246] The difference between Comparative Example 2 and Example 1 is that in step S2, the positive electrode matrix material uniformly doped with Nb and Zr is placed in a high-energy ball mill and mixed with Li2MoO4, and the mixed material is placed in a kiln for sintering in an O2 atmosphere. The sintering obtains a Li2MoO4-coated high-nickel ternary positive electrode material, excluding the first coating layer. The rest is the same as Example 1.

[0247] Table 1 Experimental parameters of Examples 1-19 and Comparative Examples 1-2

[0248] Table 2 Experimental parameters of Examples 20-21

[0249] Table 3 Performance test results of the embodiments and comparative examples

[0250] [Preparation of battery cells]

[0251] (1) Preparation of positive electrode sheets: The positive electrode active material, binder polyvinylidene fluoride (PVDF), and conductive agent (acetylene black) are dissolved in solvent N-methylpyrrolidone (NMP) in a mass ratio of 94:3:3, and the mixture is thoroughly stirred and mixed to prepare a positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and then dried, cold pressed, and cut to obtain positive electrode sheets.

[0252] (2) Preparation of negative electrode sheets: Dissolve the negative electrode active materials artificial graphite and hard carbon, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) in deionized water at a mass ratio of 90:5:2:2:1, and stir and mix thoroughly to prepare a negative electrode slurry; coat the negative electrode slurry on the negative electrode current collector copper foil, and then dry, cold press, and cut to obtain a negative electrode sheet.

[0253] (3) Isolation film: polyethylene film is used.

[0254] (4) Preparation of lithium-ion battery cells: The positive electrode sheets, separators, and negative electrode sheets are stacked and wound in order to obtain an electrode assembly; the electrode assembly is placed in an outer package, and an electrolyte solution containing lithium hexafluorophosphate as electrolyte salt is added. After packaging, standing, formation, aging, and other processes, a lithium-ion battery cell is obtained.

[0255] [Preparation of button cells]

[0256] The positive electrode active material, PVDF, and conductive carbon are added to a certain amount of NMP in a ratio of 90:5:5, stirred in a drying room to form a slurry, coated on aluminum foil, dried, and cold-pressed to form a positive electrode sheet; a lithium sheet is used as the negative electrode, the electrolyte salt in the electrolyte is LiPF6, the solvent is EC, DEC, and DMC in a volume ratio of 1:1:1, the concentration of the electrolyte salt is 1 mol / L, and the button battery is assembled in a button box.

[0257] It should be noted that the mass content of the first coating layer and the second coating layer in the positive electrode active material in the embodiments of the present application, the volume average particle size of the positive electrode active material, the cycle performance of the battery cell, etc. are common knowledge in the art, have meanings known in the art, and can be measured by test methods and instruments known in the art.

[0258] [Tests of the first and second coating layers]

[0259] The positive electrode active material particles are placed in the conventional mode, HAADF mode or ABF mode of the transmission electron microscope for observation. Using EDS element surface distribution, it can be observed that one or more elements such as W, Mo, and P are concentrated in the grain boundaries of the positive electrode active material particles, thereby determining the second coating layer and the material of the second coating layer.

[0260] Using HAADF-STEM to observe the surface of the primary particles of the positive electrode active material and perform Fourier transform analysis, the spinel phase can be observed on the surface of the primary particles, thereby confirming the first coating layer. In addition, the thickness of the first and second coating layers can also be observed.

[0261] XPS is used to characterize the relative content of each element in the positive electrode matrix material and the first coating layer, and then the concentration of Li is calculated, so that the concentration of lithium element in the positive electrode matrix material and the first coating layer can be obtained.

[0262] [Button battery initial gram capacity test]

[0263] At 2.8-4.3V, charge to 4.3V at 0.1C, then charge at 4.3V at constant voltage until the current is ≤ 0.05mA, let it stand for 2 minutes, the charge capacity at this time is recorded as C0, then discharge to 2.8V at 0.1C, the discharge capacity at this time is the initial gram capacity, recorded as D0, and the first efficiency is D0 / C0×100%.

[0264] The higher the initial efficiency, the more lithium ions can be reversibly intercalated and deintercalated. In the later stages of discharge, due to the reduction of lithium vacancies in the positive electrode active material, lithium ion diffusion within the positive electrode active material particles is slow, making lithium intercalation difficult. By constructing a first coating layer on the surface of the positive electrode active material, lithium ion diffusion is promoted, thereby improving the initial efficiency of the material.

[0265] [Lithium-ion battery cell initial gram capacity test]

[0266] Under a constant temperature environment of 25℃, let it stand for 5 minutes, discharge to 2.8V at 1 / 3C, let it stand for 5 minutes, charge to 4.25V at 1 / 3C, then charge at constant voltage at 4.25V to a current ≤ 0.05mA, let it stand for 5 minutes. The charging capacity at this time is recorded as C0, then discharge to 2.8V at 1 / 3C. The discharge capacity at this time is the initial gram capacity, recorded as D0, and the first efficiency is D0 / C0*100%.

[0267] [25 / 45℃ Cycling Performance Test of Lithium-ion Battery Cells]

[0268] At a constant temperature of 25°C or 45°C, charge the battery to 4.25V at 0.5C at 2.8-4.25V, then charge it at a constant voltage at 4.25V until the current is ≤0.05mA, let it stand for 5 minutes, and then discharge it to 2.8V at 0.5C. The capacity is recorded as D n (n=0, 1, 2...), repeat the previous process for 500 times.

[0269] [DC internal resistance of lithium-ion battery cells]

[0270] Under a constant temperature environment of 25°C, charge to 4.25V at 1 / 3C at 2.8~4.25V, then charge at constant voltage at 4.25V to a current ≤ 0.05mA. After standing for 30 minutes, discharge to 20% SOC at 1 / 3C. After standing for 60 minutes, discharge at 4C for 30 seconds. After standing for 30 minutes, charge at 4C for 30 seconds to obtain the DCR at 20% SOC.

[0271] As shown in the examples and comparative examples 1-2, by providing a first coating layer and a second coating layer on the surface of the primary particles of the positive electrode matrix material, the cycle performance of the battery cell is improved. After a certain number of cycles, the battery cell prepared with the positive electrode active material of the embodiment of the present application has a higher capacity retention rate. In addition, in combination with the examples and comparative example 1, the provision of the first coating layer in the embodiment of the present application can improve the initial efficiency of the battery cell. In combination with the examples and comparative examples 1-2, the battery cell prepared with the positive electrode active material of the embodiment of the present application has a smaller DC internal resistance.

[0272] As shown in Examples 1-4, during the preparation of the positive electrode active material, different amounts of ammonium salt were added to prepare first and second coating layers of different thicknesses. The more ammonium salt was added, the easier it was to obtain thicker first and second coating layers.

[0273] As shown in Examples 5-6, various types of ammonium salts can be used in the present application; as shown in Examples 7-8, various ammonium salts can also be mixed and added to prepare the positive electrode active material.

[0274] As shown in Examples 9-10, when the volume particle size distribution of the positive electrode active material satisfies the ratio (Dv90-Dv10) / Dv50 in the range of 1.2 to 1.35, it is beneficial for the powder of the positive electrode active material to have a higher compaction density (not shown in the table), and the compaction density can reach 3.5 g / cm 3 .

[0275] As shown in Examples 11-13 and 15, the positive electrode matrix material can be doped with a variety of different M elements to improve the corresponding performance of the positive electrode matrix material; as shown in Example 14, the positive electrode matrix material can also be doped with no M element.

[0276] As shown in Examples 16-19, the volume average particle size of the positive electrode active material is in the range of 7 μm-12 μm, and the battery cell has a good capacity retention rate.

[0277] As shown in Examples 20-21, by setting the reaction temperature of the ammonium salt and the positive electrode matrix material in the range of 400°C-600°C and the reaction time in the range of 4h-6h, the first coating layer and the second coating layer are easily prepared.

[0278] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized in that: include: A positive electrode base material, a first coating layer and a second coating layer sequentially coated on the surface of primary particles of the positive electrode base material; The concentration of lithium in the first coating layer is lower than the concentration of lithium in the positive electrode matrix material, and the second coating layer includes an ion conductor material.

2. The positive electrode active material according to claim 1, characterized in that The chemical formula of the positive electrode matrix material is Li 1+a [Ni x Co y Mn z M b ]O2, wherein M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta or Sr, 0.6≤x<1, 0≤y≤0.4, 0≤z≤0.4, 0≤a≤0.2, 0≤b≤0.1, x+y+z+b=1; optionally, 0.8≤x<1; optionally, M includes at least one of Ti, Nb, Te, V or Ta.

3. The positive electrode active material according to claim 1 or 2, characterized in that: The ion conductor material includes a compound formed by Li element and at least one of W, Mo or P element; optionally, the ion conductor material includes at least one of Li2WO4, Li2MoO4 or Li3PO4.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that The material of the first coating layer includes a transition metal oxide, and the transition metal in the transition metal oxide is the same as the transition metal in the positive electrode matrix material.

5. The positive electrode active material according to any one of claims 1 to 4, characterized in that The thickness d1 of the first coating layer satisfies: 1nm≤d1≤5nm; optionally, 1nm≤d1≤2nm.

6. The positive electrode active material according to any one of claims 1 to 5, characterized in that The thickness d2 of the second coating layer satisfies: d2≤20nm; optionally, 4nm≤d2≤10nm.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that The ratio B of the mass of the second coating layer to the mass of the positive electrode matrix material satisfies: 1000ppm≤B≤3000ppm; optionally, 1000ppm≤B≤2000ppm.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that The volume particle size distribution of the positive electrode active material satisfies: (D v 901-D v 101) / D v 501≥1.2; Optionally, (D v 901-D v 101) / D v 501≥1.

3.

9. The positive electrode active material according to any one of claims 1 to 8, characterized in that The volume particle size distribution Dv501 of the positive electrode active material satisfies: 7 μm≤Dv501≤12 μm; optionally, 8 μm≤Dv501≤10 μm.

10. The positive electrode active material according to any one of claims 1 to 9, characterized in that The first cladding layer includes a material having a spinel structure.

11. A method for preparing a positive electrode active material according to any one of claims 1 to 10, characterized in that: include: preparing a positive electrode matrix material; The first coating layer and the second coating layer are prepared on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material.

12. The method according to claim 11, characterized in that The step of preparing the first coating layer and the second coating layer on the surface of the primary particles of the positive electrode base material to obtain the positive electrode active material comprises: The positive electrode base material and ammonium salt are mixed and sintered in an inert atmosphere to obtain the positive electrode active material.

13. The method according to claim 12, characterized in that The positive electrode matrix material and the ammonium salt are mixed and sintered in an inert atmosphere to obtain the positive electrode active material, comprising: Putting the positive electrode matrix material and ammonium salt into a high energy ball mill and mixing them; The mixed positive electrode matrix material and the ammonium salt are placed in an inert atmosphere and sintered to obtain the positive electrode active material.

14. The method according to claim 13, characterized in that The rotation speed V of the high energy ball mill satisfies: 500rpm≤V≤1400rpm; optionally, 800rpm≤V≤1200rpm.

15. The method according to claim 13 or 14, characterized in that The ball milling time t1 satisfies: 0.5h≤t1≤3h; optionally, 1h≤t1≤2h.

16. The method according to any one of claims 13 to 15, characterized in that The sintering temperature T1 satisfies: 400°C≤T1≤600°C; optionally, 400°C≤T1≤500°C.

17. The method according to any one of claims 13 to 16, characterized in that The sintering time t2 satisfies: 4h≤t2≤8h; optionally, 5h≤t2≤6h.

18. The method according to any one of claims 13 to 17, characterized in that: The ammonium salt includes at least one of W, Mo or P elements; optionally, the ammonium salt includes at least one of ammonium molybdate, ammonium paramolybdate, ammonium metatungstate, ammonium phosphate, ammonium hydrogen phosphate or ammonium dihydrogen phosphate.

19. The method according to any one of claims 11 to 18, characterized in that The method for preparing the positive electrode matrix material comprises: Preparing a precursor of the positive electrode matrix material; The precursor, lithium salt, and compound containing element M are mixed and sintered to prepare the positive electrode matrix material, wherein element M includes at least one of Zr, Al, Ti, Sb, Nb, Te, Mg, Al, Ca, V, Ta, or Sr.

20. The method according to claim 19, characterized in that The molar ratio C of the lithium salt to the metal element in the precursor satisfies: 0.95≤C≤1.15; and / or, the sintering temperature T2 satisfies: 650°C≤T2≤950°C; and / or, the sintering time t3 satisfies: 10h≤t3≤20h.

21. The method according to claim 19 or 20, characterized in that Based on the total mass of the precursor, the lithium salt and the compound containing the element M, the mass content D of the compound containing the element M satisfies: 200 ppm≤D≤5000 ppm.

22. The method according to any one of claims 19 to 21, characterized in that The volume particle size distribution Dv502 of the precursor satisfies: 7μm≤Dv502≤12μm; optionally, 8μm≤Dv502≤10μm.

23. A positive electrode plate, characterized in that: The invention comprises the positive electrode active material according to any one of claims 1 to 10, and / or the positive electrode active material prepared by the method according to any one of claims 11 to 22.

24. A battery cell, characterized in that: Comprising the positive electrode sheet as described in claim 23.

25. A battery, characterized in that: Comprising the battery cell as claimed in claim 24.

26. An electrical device, characterized in that: Comprising a battery as claimed in claim 25.

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